VENTRICULAR STIMULATION DURING THE VULNERABLE PERIOD OF THE HEART CYCLE IN AN ICD-SYSTEM WITH ANTIBRADYCARDIAC DDD-PACEMAKER FUNCTION

We report a case of a 56-year-old white female with an ICD system (Ven tak AV, CPI) implanted because of repeated episodes of ventricular fib rillation and preexisting intermittent total AV-block. Several times a synchronic stimulation could be observed in the case of ventricular ex trasystole stimulating the ventricle during different times of depolar ization. The reason for undersensing of the premature ventricular comp lexes was a blanking period of 66 ms after atrial stimulation. Therefo re, the ICD was not able to sense the ventricular extrasystole and the stimulation of the ventricle occurred during the vulnerable period of the heart cycle. Induction of severe ventricular arrhythmia was not d ocumented. Because of missing programmability of the ventricular blank ing period, no possibility of a safety stimulation, and already maxima l sensitivity of the ICD, the incidence of these events could only be reduced by increasing the lower rate limit of the pacemaker and suppre ssion of the premature ventricular complexes by medication.